Thermionically emissive element



March 1954 w. ALVAREZ THERMIONICALLY EMISSIVE ELEMENT Filec} Nov. 12, 1949 LUIS W. ALVA/PEI,

INVENTOR.

A TTORNE K Patented Mar. 16, 1954 THERMI'ONICALLY EMISSIVE ELEMENT Luis W. Alvarez, Berkeley, Calif., assignor to The Rand Corporation, Santa Monica, Calif.

Application November 12, 1949, Serial No. 126,899

18 Claims.

.01 a combination of an oxide-coated sleeve and an internal heating element, where the filament or the heating element are heated by an electric current. In electronic circuits using thermionic tubes, a. significant fraction of the total power r quired is used for heatin such thermionically emissive cathodes, and, in some important applications, especially Where the factor of weight required to supply such fraction of power is disadvantageous, heating the cathode without such weight would be highly desirable.

Accordingly, it is an object of my invention to provide a thermionically emissive element which is directly heated and which is useful as the cathode for thermionic tubes, requiring no elec tric power for heating the thermionically emissive cathode.

Other objects and advantages of my invention will be apparent to those skilled in the art to which my invention appertains from the following description, taken in conjunction with the accompanying drawing.

In accordance with my invention, the thermionically emissive cathode is heated directly, without the use of an electric current, by means of a radioactive material so associated and arranged with respect to the thermionically emissive element as to heat it and cause it to emit electrons. The cathode, whether of the incandescent filament type ora combination of a sleeve coat d w h t ermionically emissive mate rial, is heated with the radioactive material. This may be accomplished, for example, in accordance with one embodiment of my invention, by making the cathode filament or coated sleeve of hollow tubing, which tubing contains the radioactive material, that is, the tubing may be filled with the radioactive material.

The radioactive substance may be in any suitable form, such as chemical element, a chemical compound, or an alloy. Various radioactive elements, in any such suitable form, with different kinds and intensities of radiation, may be used.

For the purposes of my invention, the alphaemitting radioactive elements are preferred, particularly polonium. The alpha particles cause a heating of the thermionic emitter without the undesirable effects of beta and gamma emission, as pointed out below. The beta-emitting radioactive elements may also be used, but, for such radioactive substances, it will usually be found desirable to appropriately shield the functional tube elements from the beta rays which pass through the thermionically emitting element to avoid any resulting high noise level. This may be done by enclosing the beta-emitting radioactive substance in a shielding material which is in heat transfer relationship with the thermionically emissive element, so that when the shielding material is heated by absorption of the beta radiation, the heat is transferred to the thermionically emissive element to cause the desired emission of electrons therefrom. Such beta-emitting radioactive substances particularly include strontium, yttrium and cerium. Radioactive elements which include gamma radiation, in addition to alpha, beta, or both, are less desirable because of the well-known hazards associated with gamma radiation.

It is to be emphasized that the radioactive material used in accordance with my invention serves only as a source of heat, and for the purpose of heating the t-hermionically emissive element or material to cause thermionic emission of electrons by the thermionically emissive material of the cathode surface.

My invention will be further illustrated by reference to specific examples described below in conjunction with the accompanying drawing, in which:

Figure 1 shows a thermionically emissive element heated solely with a radioactive material, in accordance with my invention, and

Figure 2 schematically shows a conventional triode having a thermionicallv emissive cathode heated with radioactive material, in accordance with my invention.

In Figure 1 is shown a base or core material I, which may be nickel, nickel with a few per cent of silicon or cobalt, Monel metal, or platinum, preferably coated with a thermionically emissive material 3 such as metal oxides used for this purpose, for example, barium oxide, strontium oxide, a mixture thereof and the like. As shown, the base material I is in the form of a hollow tube with suitable cap or closure 2. The base tube 1 is filled with a sufficient quantity of polonium or other radioactive material to heat the tube I and thermionically emissive material 3 to cause the thermionic emission of electrons therefrom.

It will be understood, of course, that the radioactive material and the quantity thereof, will be chosen so as not to seriously overheat the thermionically emissive element or the thermionic tube in which used and yet give heating for a sufliciently satisfactory length of time, which length of time will, of course, be related to the half-life of the radioactive material used. Also, for applications where weight is especially undesirable, the radioactive substance should have a sufficiently high energy available for heating the thermionically emissive element per unit weight of the substance used; that is, the radioactive substance should be chosen with respect to element and form to give the desired heating of the thermionically emissive element without adding undesirable weight. It is a significant feature of my invention that, in accordance therewith, it is possible to accomplish this highly desirable result.

When beta-emitting radioactive substances are used, in order to prevent an increase in noise level arising from high-energy electrons originating in the radioactive process itself, a shield of suitable absorbing material may surround the radioactive substance to absorb such high-speed electrons and be heated thereby. Such a shield would be arranged in thermal contact with the thermionically emitting element. In Figure 1, for example, the base material or sleeve 5 may be made of suitable shielding material to perform the functions of shielding, as described above, as well as supporting the transferring heat to the thermionically emissive material 3. Also, if desired, a separate internal tube of shielding material (not shown on the: drawing) may be inserted within tubing I and this shielding material filled with the radioactive substance.

Figure 2 shows a conventional triode having a thermionically emissive cathode, in accordance with my invention. The usual gass or other tube envelope is shown at E, with plate P having lead L-3, grid G having lead L-Z, and cathode C having lead L-i. In accordance with my invention, the cathode C comprises a tube 5 of thermionically emissive material containing, or filled with, the radioactive material polonium, shown at 6. The cathode C may be made as described in connection with Figure 1 above. Since the cathode C is heated entirely by means of the radioactive material and not by an electric current, no lead lines and no electric power is required for such heating.

The specific examples given above are for the purpose of illustrating my invention, and my invention includes other modifications within the scope of the following claims.

I claim:

1. A thermionically emissive element heated 0 a heating and consequent thermionic emission from said thermionically emissive material.

2. A thermionically emissive element heated solely with a radioactive substance, comprising a thermionically emissive material and radioactive material in such relation thereto that radioactive emission from said radioactive material causes a heating and consequent thermionic emission from said thermionically emissive material.

3. A thermionically emissive element comprising a hollow container, the surface of which is capable of emitting electrons when heated, and the interior of which contains a radioactive substance for heating said container to cause emission of electrons from said surface.

4. A thermionically emissive element as defined in claim 1 in which said radioactive substance is an alpha-emitter.

5. An element as defined in claim 4 in which said alpha-emitter is polonium.

6. An element as defined in claim 4 in which said radioactive substance emits only alpha particles.

'7. A thermionically emissive element as defined in claim 1 in which said radioactive substance is a beta-emitter.

8. An element as defined in claim 7 in which said beta-emitter is strontium.

9. An element as defined in claim '7 in which said beta-emitter is yttrium.

15. An element as defined in claim 7 in which said beta-emitter is cerium.

11. A thermionically emissive element as defined in claim 1 having a shield for high-speed beta electrons in heat transfer relationship with the thermionically emissive material.

12. A thermionically emissive element as defined in claim 2 in which said radioactive substance is an alpha-emitter.

13. An element as defined in claim 12 in which said alpha-emitter is polonium.

14. An element as defined in claim 12 in which said radioactive substance emits only alpha particles.

15. A thermionically emissive element as defined in claim 2 in which said radioactive substance is a beta-emitter.

16. An element as defined in claim 15 in which said beta-emitter is strontium.

17. An element as defined in claim 15 in which said beta-emitter is yttrium.

18. An element as defined in claim 15 in which said beta-emitter is cerium.

LUIS W. ALVAREZ.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,523,013 Greenslade Jan. 13, 1925 1,530,555 Greenslade Mar. 24, 1925 2,032,545 McElrath Mar. 3, 1936 2,449,113 Fruth Sept. 14, 1948 

1. A THERMIONICALLY EMISSIVE ELEMENT HEATED WITH A RADIOACTIVE SUBSTANCE, COMPRISING A THERMIONICALLY EMISSIVE MATERIAL AND RADIOACTIVE MATERIAL IN SUCH RELATION THERETO THAT RADIOACTIVE EMISSION FROM SAID RADIOACTIVE MATERIAL CAUSE A HEATING AND CONSEQUENT THERMIONIC EMISSION FROM SAID THERMIONICALY EMISSIVE MATERIAL. 